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  <title>Document</title>
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<body>
  
  <!-- 
    1. js 命名出现  字母 数字 _ $， 不能数字开头

    2. 见名知意
   -->

   <script>
     var test = 'qwer'

     var username = 'zs'

     var chinaJiNan = '济南'

     var testAge = 19

     console.log($1)
   </script>
</body>
</html>